System and method for electrical impedance tomography of an object, and an impedance measurement unit

Abstract

A system for electrical impedance tomography comprises: a plurality of electrodes; a plurality of impedance measurement units, each being associated with two or more electrodes, and wherein each impedance measurement unit comprises a current generator for generating a stimulation current between the electrodes and an amplifier for amplifying a measurement voltage between the electrodes; wherein the system is configured to perform a plurality of impedance measurements, wherein, for each impedance measurement, one impedance measurement unit is set in a stimulation mode for providing a stimulation current into the object, and wherein the impedance measurement unit being set in the stimulation mode is switched among the plurality of impedance measurement units, and wherein each impedance measurement unit is configured to be set in a calibration mode during at least one of the plurality of impedance measurements.

The invention claimed is: 
     
       1. A system for electrical impedance tomography of an object, said system comprising:
 a plurality of electrodes configured to be attached to the object; 
 a plurality of impedance measurement units, wherein each impedance measurement unit is associated with two or more electrodes of the plurality of electrodes, and wherein each impedance measurement unit comprises a current generator for generating a stimulation current between the electrodes associated with the impedance measurement unit and an amplifier for amplifying a measurement voltage between the electrodes associated with the impedance measurement unit; 
 wherein the system is configured to perform a plurality of impedance measurements, wherein, for each impedance measurement, one impedance measurement unit among the plurality of impedance measurement units is set in a stimulation mode for providing a stimulation current into the object between the electrodes associated with the one impedance measurement unit, and wherein the impedance measurement unit being set in the stimulation mode is switched among the plurality of impedance measurement units between different measurements in the plurality of impedance measurements, and 
 wherein each impedance measurement unit is configured to be set in a calibration mode during at least one of the plurality of impedance measurements for calibration of the impedance measurement unit during electrical impedance tomography measurements. 
 
     
     
       2. The system according to  claim 1 , wherein each impedance measurement unit is configured to be set in the stimulation mode during at least one impedance measurement of the plurality of impedance measurements. 
     
     
       3. The system according to  claim 1 , wherein, in the calibration mode, the impedance measurement unit is configured to calibrate a current generated by the current generator of the impedance measurement unit. 
     
     
       4. The system according to  claim 3 , wherein the impedance measurement unit comprises unity gain buffers configured to be connected to nodes on opposite sides of the current generator in calibration measurements for calibrating the current generated by the current generator. 
     
     
       5. The system according to  claim 1 , wherein, in the calibration mode, the impedance measurement unit is configured to calibrate a gain of the amplifier. 
     
     
       6. The system according to  claim 1 , wherein each impedance measurement unit comprises a reference resistor, which is configured to be connected to the current generator in the calibration mode for calibration of the impedance measurement unit. 
     
     
       7. The system according to  claim 1 , wherein each impedance measurement unit is associated with two neighboring electrodes in the plurality of electrodes, and wherein an electrode is shared by two neighboring impedance measurement units in the plurality of impedance measurement units. 
     
     
       8. The system according to  claim 7 , wherein, for a subset of impedance measurements in the plurality of impedance measurements, the subset being acquired at a single point in time, two impedance measurement units being arranged on opposite sides of and neighboring to the one impedance measurement unit being set in the stimulation mode are configured to be set in the calibration mode. 
     
     
       9. The system according to  claim 1 , wherein, for a subset of impedance measurements in the plurality of impedance measurements, the subset being acquired at a single point in time, each impedance measurement unit not being in the stimulation mode or the calibration mode is set in a measurement mode for measuring a voltage between the electrodes associated with the impedance measurement unit. 
     
     
       10. The system according to  claim 1 , wherein the system is configured to set one of the impedance measurement units in the plurality of impedance measurement units as a master impedance measurement units and remaining impedance measurement units as slave impedance measurement units, wherein the master impedance measurement unit is configured to communicate with the slave impedance measurement units for controlling operation of the slave impedance measurement units. 
     
     
       11. The system according to  claim 10 , wherein the master impedance measurement unit is configured to generate a master clock signal and to transmit the clock signal to the slave impedance measurement units for synchronizing clocks of the plurality of impedance measurement units. 
     
     
       12. An electrical impedance tomography apparatus comprising the system according to  claim 1 , wherein the apparatus is configured to be worn by a subject and wherein the apparatus is configured to continuously monitor bioimpedance of the subject while the apparatus is worn. 
     
     
       13. A method for electrical impedance tomography of an object by a system comprising a plurality of electrodes and a plurality of impedance measurement units wherein each impedance measurement unit is associated with two electrodes of the plurality of electrodes, said method comprising for performing an impedance measurement:
 setting one impedance measurement unit into a stimulation mode for providing a stimulation current into the object between the electrodes associated with the one impedance measurement unit; 
 setting impedance measurement units on opposite sides of and neighboring to the one impedance measurement unit being set in the stimulation mode into a calibration mode for calibration of the impedance measurement unit; and 
 setting impedance measurement units not being in the stimulation mode or the calibration mode into a measurement mode for measuring a voltage between the electrodes associated with the impedance measurement unit.